Content addressable memories (CAMs) are generally used to compare input data to data stored in a memory array, and to return an indication associated with a matching of the input data to the stored data. This indication may include the matching memory location. CAMs are frequently used in applications which require relatively fast data searching or pattern matching, such as, for example, in database storage, network routing, speech processing, image processing, among other numerous applications.
CAMs are generally divided into two groups, binary CAMs and ternary CAMS (T-CAMs). In binary CAMs, only two types of bits are stored in the memory cells, a “0” or a “1”. A CAM search in the memory array will yield a positive matching result when the value and the position of each bit in the input data are exactly matched in the stored data. In ternary CAMs, a third bit may be stored in the memory cells which is a “don't care” bit (represented by an “x”). In this CAM, a search in the memory array will yield a positive matching result if the value and position of each bit in the input data is exactly matched in the stored data, except for memory cells which store the “don't care” bit which may match both a “0” or a “1” in the input data.
CAM cells typically have included either NOR-type memory cells or NAND-type memory cells using SRAM or DRAM technology. In recent years, CAM technology has been moving towards the use of non-volatile memories (NVMs) such as NAND and NOR flash memories, among other type of NVMs. Examples of CAMs using these types of NVMs are described in US Patent Publication No US 2015/0131383, assigned to the common assignee of the present application.